The bacterium Bordetella pertussis is the causative agent for whooping cough, a respiratory disease that can be severe in infants and young children. The clinical course of the disease is characterised by paroxysms of rapid coughs followed by inspiratory effort, often associated with a characteristic ‘whooping’ sound. In serious cases, oxygen deprivation can lead to brain damage; however the most common complication is secondary pneumonia.
Whooping cough is usually considered to be caused by B. pertussis, but occasionally B. parapertussis is isolated from patients with typical signs and symptoms of whooping cough. B. parapertussis infection is of lower frequency than B. pertussis with 5-10% of whooping cough being associated with B. parapertussis (Mertsola (1985) Eur J Clin Microbiol 4; 123; Lautrop (1971) Lancet 1(7711) 1195-1198). B. parapertussis is associated with mild clinical symptoms which, combined with its serological cross-reactivity with B. pertussis, makes B. parapertussis difficult to diagnose.
The first generation of vaccines against B. pertussis were whole cell vaccines, composed of whole killed bacteria. These were introduced in many countries in the 1950s and 1960s and were successful at reducing the incidence of whooping cough. A problem with whole cell B. pertussis vaccines is the high level of reactogenicity associated with them. A cellular vaccines containing purified B. pertussis proteins are less reactogenic and have been adopted for the vaccination programmes of many countries. A cellular vaccines typically containing pertussis toxin (PT), filamentous haemagglutinin (FHA) and quite often pertactin (PRN), are widely used and provide effective protection from the severity of whooping cough.